units: add missing header

BITS_PER_BYTE is defined in bits.h.

Link: https://lkml.kernel.org/r/20231128174404.393393-1-andriy.shevchenko@linux.intel.com


Fixes: e8eed5f7 ("units: Add BYTES_PER_*BIT")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Damian Muszynski <damian.muszynski@intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>